Electrical contact brush with a corrosion resistant shunt connection



Sept. 8, 1964 R. R. PAXTON ETAL 3,148,295 ELECTRICAL CONTACT BRUSH WITH A CORROSION RESISTANT SHUNT CONNECTION Filed Feb. 20. 1961 Howard T- Hu burl INVENTORS Ral uh R.PaIt-o7v Paul .I. Sor

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United States Patent 3,148,295 ELECTRICAL CONTACT BRUSH WITH A CGRRO- SION RESISTANT SHUNT CONNECTIGN Ralph R Paxton, Beminger Township, Eik County, and

Paul J. Song and Howard T. Hulburt, St. Marys, Pa.,

assignors to Pure Carbon Company, Inc, St. Marys,

Pa., a corporation of Pennsylvania Filed Feb. 20, 1961, Ser. No. 90,490 7 Claims. (Cl. 310249) This invention relates to electrical contact brushes and particularly to a contact brush with a flexible corrosion resistant shunt connection.

There are many installations in the steel and chemical industries where electrical machinery is operated in a very corrosive atmosphere. Such atmospheres have a particularly bad eflect upon the lead wires known as shunts which connect a terminal such as a brush or an electrode to a terminal connecting the same to the rest of the circuit. In order to provide minimum resistance to flexing, the shunts are in the form of conductors made up of many metal strands or wires of small diameter. The electrical current passing through these shunts keeps them well above ambient temperatures and the constant flexing due to the rotation or other motion of the machinery continuously opens up the shunt strands to the corrosive atmosphere and in many instances the shunts have become useless due to corrosion long before the brush itself is worn out. Corrosion of the fine wire strands of the shunt reduces the current carrying capacity and the increased resistance increases the heating of the stranded conductor until it becomes necessary to replace the brush or electrode. When it is necessary to shut down the machinery to replace a brush or electrode the expense incurred includes the cost of lost operating time as well as the cost of the new brush or electrode which must be substituted for the old one. Since a shunt may be attached to an electrode in exactly the same way as it is attached to a brush, the term brush as herein used should be understood to include other terminals such as electrodes of similar construction. A number of attempts have been made to alleviate this difliculty. In some instances silver wires have been substituted for copper wires in the shunt and in other instances nickel plated copper wires have been substituted for the copper Wires usually employed. The cost of the silver wires and plated wires for a given current capacity is substantially higher than the cost of copper wire and in addition the plated wires are necessarily of greater diameter, which results in a stiifer shunt connection which decreases the freedom of movement of the brush in the brush holder. Attempts have been made to protect the copper wire by means of varnishes and paints but such attempts have been unsatisfactory because varnish and pain coatings soon become brittle and crack. Rubber insulation has been provided for the stranded conductor but this has resulted in an objectionable decrease in flexibility and has not provided the desired protection for the stranded conductor.

In shunt connections which are subjected to considerable heat in an atmosphere containing corrosive vapors, deterioration of the stranded conductors can be prevented only by hermetically sealing the stranded conductors from the surrounding atmosphere. Several polymerization products are known which are resistant to corrosive vapors and that withstand relatively high temperatures such as from 300 F. to 500 F. for extended periods of time without deterioration, such for example as the fluorinated elastomers, tetrafluoroethylenes, often referred to as the 'I'FE elastomers, certain of which are sold under the trade name Teflon, chlorotrifluoroethylenes known as CTFE elastomers, certain of which are sold under the 3,148,295 Patented Sept. 8, 1964 trade name Kel-F, and silicone elastomers. Because of the constant flexing to which the shunt cable is subjected, it is essential that the protective sheath be firmly attached to the brush body by a bond which is not seriously weakened eithed by the heat to which the shunt is subjected or by continual flexing during operation. Commercially available silicone elastomer-s such as the halogenated aryl silicones, the diorgano silicones and methyl silicone rubbers are chemically inert, are elastic and flexible at high temperatures, and bond well to metals, ceramic materials, textile fabrics and other elastomers.

In order to provide a permanent fluid-tight and flexible bond between the protective sheath and the brush body, it has been found desirable to employ a silicone elastomer preferably for the entire sheath and particularly at the joint between the protective sheath and the brush body. When a protective sheath is provided the stranded conductor may be composed of wires that are loosely connected by braiding or by bunching so that they are free to move relatively when the conductor is flexed and oifer but little resistance to flexing. In order to avoid an objectionable decrease in flexibility due to the protective sheath it is desirable that the stranded conductor be free from adhesion to the sheath except immediately adjacent the brush and conductor terminal. It is therefore preferred that the portion of the sheath covering the stranded conductor from the brush to the terminal be in the form of a preformed tube that loosely fits over the conductor. The tube may be an extruded tube formed of a suitable heat resistant elastomer or may be in the form of a fabric or fiber reinforced tube. The sheath is completed by joining the ends of the insulating tube to the brush and to the conductor terminal by means of bonds composed of an uncured silicone elastomer which when cured will form an impervious flexible and elastic bond to the brush, the conductor terminal and the tube. If the material of the tube is not compatible with the silicone elastomer a good bond between the tube and silicone elastomer may be provided by providing the end portions of the tube with a priming coat composed mainly of an elastomer compatible with that of the tube but containing a small amount of a silicone elastomer. If a fabric sleeve is employed the silicone elastomer may be applied to the sleeve throughout its length. The uncured silicone elastomer may be applied to the shunt in the form of a solution or in the form of a latex suspension. The latex may be applied by spraying, brushing or by means of a squeeze bottle to provide a relatively thin coating on the ends of the previously applied tube or over the entire length of a fabric sleeve and to seal the openings to the sockets in the brush body and conductor terminal into which the ends of the shunt cable extend. When cured, the coating is firmly bonded to the tube or sleeve, the conductor terminal and the brush body.

In order to provide a stronger and more elastic bond between the joint and protective sheath, the socket formed in the brush body which receives the stranded conductor is preferably enlarged outwardly of the electrical connection between the cable and brush to provide a Well surrounding the cable which receives the sealing elastomer which when cured is bonded to the Wall of the socket, thereby providing a large bonded area and a relatively thick body of elastomer surrounding the said conductor which, by reason of its elasticity, permits flexing of the shunt without deterioration of the bond between the protective sheath and the brush body.

Reference should be had to the accompanying drawings forming part of this specification in which:

FIGURE 1 is a front elevation showing an electrical contact brush and a corrosion resistant shunt connection embodying the invention, a portion of protective sheath being broken away to show the stranded shunt cable;

FIG. 2 is a side elevation of the shunt connection with a portion broken away to show the joint between the brush body and the protective sheath;

FIG. 3 a side elevation of a modified form of connection with a portion of the brush body and protective sheath broken away and shown in section;

FIG. 4 is an elevation showing a modified form of connection in which a cable with an attached insulating covering is employed as the shunt connection; and

FIG. is an elevation partially in section showing the elastic seals connecting the insulation to the conductor terminal and the brush body.

In FIGS. 1 and 2 of the drawings, the invention is shown applied to a brush 1 which may be composed of carbon or a mixture of carbon and finelydivided metal such as copper. The brush 1 has conductor receiving sockets 2 and 3 opening to its top face which receive stranded conductors 4 and 5 each composed of a large number of small diameter wires of a suitable metal such as copper. The stranded conductors 4 and 5 are connected at their outer ends to a conductor terminal 6 and form with said terminal a shunt connection for the brush. The terminal 6 which is formed of a suitable metal, has a conductor receiving socket 7 in which the outer ends of the cables 4 and 5 are electrically joined to the terminal 6 by suitable means such as a soldered connection.

The inner ends of the stranded conductors 4 and 5 may be electrically connected to the brush 1 by means of a tamped connection 8 in the bottom portion of the sockets 2 and 3. A powdered conductive material such as an amalgam is tamped tightly around the end portions of the conductors 4 and 5 in the bottom portion of each of the sockets 2 and 3 and the brush body is heated to fuse the conductive material and provide a low resistance connection between each conductor and the brush body. Each of the sockets 2 and 3 has an enlarged upper end 9 above the electrical connection between the conductors and the brush body.

In :order to provide a protective sheath which will hermetically seal the stranded conductors of the shunt from the surrounding atmosphere, a tubular fabric sleeve 10 such as a cotton fabric sleeve, is placed upon the portion of each of the stranded conductors extending between the brush body l and the conductor terminal 6. The fabric sleeves may be preformed and slipped upon the conductors before they are connected to the conductor terminal or they may be applied to the conductors after the electrical connections to the brush body and conductor terminal are made. The fabric lining for the sheath is desirable not only to provide a stronger covering for the wire cables, but also in order to prevent impregnation of the stranded conductor with the insulating material and adhesion of the conductor strands to one another and the protective sheath which would lessen the flexibility of the shunt. The wires of the shunt are preferably loosely braided or bunched so as to provide minimum resistance to flexing and a greater degree of flexibility is obtained when the wire strands are substantially free from adherence to one another and to the sheath except immediately adjacent their connection to the brush body and to the conductor terminal.

A coating 11 of a suitable flexible heat resistant elastomer is applied to the exterior of the sleeve 10 and has end portions 12 and 13 that seal the sockets of the conductor terminal and brush body. The heat resistant and corrosion resistant coating is preferably a silicone elastomer because of the fact that such elastomers when cured in contact with a metal fabric or ceramic material, will form a firm bond with such metal, fabric or ceramic material and also for the reason that such elastomers may be compounded to provide high heat and corrosion resistance, together with high elasticity and flexibility.

Either silicone resins or silicone rubbers may be employed, but silicone rubbers are preferred because of their superior bonding characteristics. The el-aston'ler coating 11 may be applied to the fabric sleeve and to the brush body and terminal conductor in the form of a solution or in the form of a latex suspension, but the suspension is preferred because of the fact that a greater concentra tion of solids may be obtained in such a suspension and there is less shrinkage of the coating upon evaporation of the liquid in which the particles of elastorner are suspended. The sleeves lltl extend from the brush 1 to the terminal 6 and preferably have their inner ends within the enlarged ends 9 of the brush socket so that the uncured elastorner coating 11 contacts the conductor strands only immediately adjacent the points of attachment of the stranded conductor to the brushand terminal.

As shown in MG. 2, the portion 13 of the coating 11 fills the large upper portions 9 of the sockets 2 and 3 and may extend over portions of the top face of the brush body as shown in FIG. 1 to provide a relatively large bonded area between the brush body and the protective sheath. At the terminal end the end portion 12 of the coating 11 covers the portion of the terminal 4- around the socket '7 to completely seal the terminal ends of the cables. When subjected to cuning heat, the silicone elastomer is firmly bonded to both the brush body and terminal and provides a thin, flexible heat resistant impervious covering for the stranded conductors between the brush body and terminal.

in FIG. 3 of the drawing a modified form of connection is shown in which a brush body 14 and a conductor terminal 15' are connected by a stranded conductor 16. The brush body, terminal and conductor may be similar to the brush body, terminal and conductor previously described but the connection of the conductor to the brush is of a different type. The brush body has a bore 17 opening to its top face which forms a conductor receiving socket and a counterbore 18 provides the socket with an enlarged upper end portion. A transverse bore 19 intersects the bore 17 and is provided with counterbores 20 and 21 at its opposite ends. The electrical connection between the brush body and shunt cable is formed by clamping the end of the stranded conductor 16 against the brush body by means of a tubular rivet 22 which has its ends 23 and 24 spun over metal washers 25 and 26 in the counterbores 2t) and 21. The washer 25 engages the conductor 16 to clamp it against the wall of the counterbore and the washer 26 engages the bottom of. the counterbore 24!. A protective sheath 27 is formed by applying a latex covering to the stranded conductor as in the modification first described. A fabric sleeve may be provided within the sheath if desired or the sheath may be applied directly to the exterior of the cable and bonded to the brush body and conductor terminal by curing in contact therewith. When the fabric sleeve is omitted, the latex is applied in the form of a thick paste which does not penetrate into the spaces between the conductor strands sufficiently to adhere the strands to one another to an extent such as to materially reduce flexibility. To insure against the entry of corrosive vapors through the lateral openings, the counterbores 2t) and 21 at the opposite ends of the rivet 22 may be filled with a suitable sealant which may be of the same material as the sheath 27.

In FIGS. 4 and 5 of the drawings, a modified construction is shown in which a brush body 31 and a terminal 2&2 are connected by a stranded conductor 33. The conductor terminal 32 has a socket forming portion 34 that receives the outer end of the stranded conductor 33 and a preformed insulating tube 35 covers the cable from the terminal 32 to the brush body 31. The tube 35 may be composed of any flexible heat resistant elastomer and may be either an extruded tube or a fabric reinforced tube. This tube is slipped on the stranded conductor before the conductor terminal is attached thereto. The

brush 3 has a socket 36 opening to its top face which has an enlarged upper end 37.

The electrical connection between the cable and brush is made in the lower portion of the socket 36 below a large upper end 37 thereof. The outer end 38 of the tube 35 is slit and reduced in diameter to closely conform to the stranded conductor 33 immediately adjacent the socket portion 34 of the terminal 32. A band of sealing material 39 surrounds the reduced outer end 38 of the tube 35 and the adjacent portion of the terminal 32. This band of sealing material may be applied in the form of a latex and bonded to the tube 35 and terminal 32 when it is cured in situ. A second band of sealing material 40 surrounds the inner end of the insulating tube 35 and fills the enlarged upper end of the socket 36, the band 40 being bonded to the tube and to the brush body by curing in situ. The sealing material for the bands 39 and 40 is preferably a silicone rubber while the insulating tube may be formed of any elastomer which has the necessary flexibility, chemical inertness and heat resistance.

If the insulating tube 35 is formed of an elastomer that is not compatible with the silicone rubber such as a fluorocarbon elastorner, a good bond may be provided by applying to the ends of the tube a priming coat which will bond to the material of the tube end which contains a small amount of silicone rubber.

Since brushes may vary greatly in composition, it may in some instances be desirable to provide the brush with a thin priming coat composed of an elastomer which will bond Well to the brush body and to the elastomer which forms the seal. In order to provide a strong fluid tight bonded connection between the brush body and the elastic sheath it is usually desirable that the sheath extend into the brush socket and that it be bonded to the wall of the socket that surrounds the conductor. As herein shown, the socket is enlarged at its upper end to increase the area of contact between the sheath and brush body, but it is apparent that similar results may be obtained with sockets of various shapes and dimensions and that an adequate bonding area may be provided entirely upon the top face of the brush body.

The heat resistant elastomers employed in the protective sheath are preferably so compounded that they are readily flexible and so that they will retain their flexibility and strength when subjected for long periods of time to temperatures above 200 F and be capable of withstanding temperatures up to 500 F. for shorter periods.

Elastomers suitable for the protective sheath may be of the type which require the application of heat for curing but for economy and convenience We prefer a room temperature curing organopolysiloxane such as disclosed in the patent to Berridge, 2,843,555, granted July 15, 1958.

It is to be understood that in accordance with the provisions of the patent statutes, variations and modifications of the specific devices herein shown and described may be made Without departing from the spirit of the invention.

What we claim is:

1. A corrosion resistant shunt connection comprising terminals each having a conductor receiving socket, a

stranded conductor, said conductor having its ends received in said sockets and electrically connected to said terminals within said sockets, and means hermetically sealing said stranded conductor from the surrounding atmosphere comprising a flexible heat resistant non-conductive sheath covering said cable between said terminals and closing the openings to said sockets, said sheath comprising a heat and corrosion resistant elastomer that is bonded to said terminals around each of said openings.

2. A corrosion resistant shunt connection as set forth in claim 1 in which the portions of the sheath bonded to the terminals are composed of a flexible and elastic silicone elastomer.

3. A corrosion resistant shunt connection as set forth in claim 2 in which the electrical connection between the stranded conductor and one terminal is spaced inwardly from the open end of the conductor receiving socket, and in which the elastomer fills the said socket outwardly of said connection.

4. A corrosion resistant shunt connection as set forth in claim 2 in which the silicone elastomer is an organopolysiloxane that is curable at room temperature.

5. A corrosion resistant shunt connection as set forth in claim 2 in which the protective sheath comprises a tube of flexible heat resistant material covering the stranded conductor between the terminals and in which the sheath is bonded to the terminals by bands of silicone elastomer bonded to the brush body and terminal and to said insulating tube.

6. A corrosion resistant shunt connection as set forth in claim 2 in which the portion of the sheath covering the cable between the terminals is a thin flexible tube composed of a sleeve of textile fabric covered by a thin layer of a heat resistant elastomer.

7. A corrosion resistant shunt connection comprising a brush body and a conductor terminal each having a conductor receiving socket, a stranded conductor composed of small diameter loosely connected wire strands, said conductor having its ends received in said sockets and electrically connected to said body and terminal within said sockets, and means hermetically sealing said stranded conductor from the surrounding atmosphere comprising a flexible heat resistant non-conductive sheath covering said conductor between the brush and conductor terminal closing the openings to said sockets and bonded to said brush body and terminal, said stranded conductor being substantially free from adhesion to said sheath except immediately adjacent said brush body and said terminal.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A CORROSION RESISTANT SHUNT CONNECTION COMPRISING TERMINALS EACH HAVING A CONDUCTOR RECEIVING SOCKET, A STRANDED CONDUCTOR, SAID CONDUCTOR HAVING ITS END RECEIVED IN SAID SOCKETS AND ELECTRICALLY CONNECTED TO SAID TERMINALS WITHIN SAID SOCKETS, AND MEANS HERMETICALLY SEALING SAID STRANDED CONDUCTOR FROM THE SURROUNDING ATMOSPHERE COMPRISING A FLEXIBLE HEAT RESISTANT NON-CONDUCTIVE SHEATH COVERING SAID CABLE BETWEEN SAID TERMINALS AND CLOSING THE OPENINGS TO SAID SOCKETS, SAID SHEATH COMPRISING A HEAT AND CORROSION RESISTANT ELASTOMER THAT IS BONDED TO SAID TERMINALS AROUND EACH OF SAID OPENINGS. 